Filter off-by-default RUF014 out of schema (#5832)
**Summary** Previously, `RUF014` would be part of ruff.schema.json
depending on whether or not the `unreachable-code` feature was active.
This caused problems for contributors who got unrelated RUF014 changes
when updating the schema without the feature active.
An alternative would be to always add `RUF014`.
**Test plan** `cargo dev generate-all` and `cargo run --bin ruff_dev
--features unreachable-code -- generate-all` now have the same effect.
